The invention relates to an arrangement for open-end rotor spinning including an opening roller, a spinning rotor and having a fiber feeding duct connecting the opening roller and the spinning rotor. The fiber feeding duct starts at the circumference of the opening roller with a cross-section adapted to the working width of the opening roller and tapers to its mouth which is disposed opposite a sliding surface of the spinning rotor which expands conically toward a fiber collecting groove which is followed by a rotor bottom by means of which the rotor is fastened on a shaft. The mouth of the fiber feeding duct is disposed in a projection projecting into the rotor, this projection, together with the open edge of the rotor, forming an overflow gap for the transport air and being part of a cover which covers a rotor housing receiving the rotor and connected to a vacuum line.
For a perfect rotor spinning operation, it is endeavored that the fibers fed in the fiber feeding duct arrive on the sliding wall of the rotor, on the one hand, at a sufficient distance from the fiber collecting groove and, on the other hand, also at a sufficient distance from the open end.
As a result, it is to be achieved that a sufficient path is available on the sliding surface so that during their movement toward the fiber collecting groove, the fibers can still be drawn. On the other hand, it is to be avoided that the fibers are taken along by the transport air flowing off over the open rotor edge. In modern open-end rotor spinning machines, there is a tendency toward progressively higher rotor speeds and at the same time progressively smaller spinning rotors. Spinning rotors are currently known which have a diameter in the area of the fiber collecting groove of less than 36 mm. Because of these small dimensions, the maintaining of the above-mentioned conditions becomes more difficult. It should be endeavored to guide the fibers as precisely as possible to one point; i.e., in an almost punctiform manner. This requires a very small mouth for the fiber feeding duct. However, as a result of a small mouth of the fiber feeding duct, the amount of air that can be taken in diminishes so that difficulties arise during the fiber transport and the risk occurs that dirt remains hung up particularly in the starting area of the fiber feeding duct. In addition, the overflow gap between the insert and the open rotor edge becomes smaller so that increased flow rates of the flowing-off air occur there which increases the danger of a taking-along of fibers.
In order to solve some of the described problems, it has been contemplated according to German Published Examined Patent Application (DE-A) 37 04 460 to enlarge the mouth of the fiber feeding duct in the circumferential direction of the spinning rotor, but to keep it as small as possible in the axial direction, i.e., in the longitudinal direction of the sliding surface of the rotor.
It has also been contemplated according to German Published Examined Patent Application (DE-A) 37 30 706 to open up the fiber feeding duct starting from the mouth area opposite the sliding surface by means of a lateral slot so that the cross-section determining the taken-in amount of air is placed from the mouth back into an area with a larger cross-section.
It has been contemplated according to German Published Examined Patent Application (DE-A) 31 20 877 to prevent or at least limit a depositing of fine dirt particles, particularly dust, in the rotor, by separating the transport air flow from the fibers before the entry into the spinning rotor and discharging it. The fine particles, which have a smaller mass than the fibers, are taken along by the transport air flow.
It has been contemplated according to German Published Examined Patent Application (DE-A) 26 15 505 to provide ventilating bores in the rotor bottom of the rotor of the spinning rotor, the axes of the ventilating bores extending approximately in parallel with respect to the axis of the spinning rotor. These ventilating bores have the purpose of influencing the pressure conditions in the interior of the spinning rotor and thus also the flow conditions.
It is an object of the invention to provide an arrangement for open-end rotor spinning of the initially mentioned type in which, without any significant increase of the vacuum, a sufficient amount of air is taken in also in the case of small spinning rotors and in which nevertheless a strong bundling of the fed fibers is obtained without the arising of any problems with respect to the removal of the transport air.
This object is achieved according to preferred embodiments of the invention in that the fiber collecting groove of the rotor has a diameter of maximally 33 mm, in that the mouth of the fiber feeding duct has a cross-section of maximally 20 mm.sup.2, in that the fiber feeding duct, in an area located outside the rotor, is provided with at least one bypass opening connected to a vacuum source, and in that the rotor bottom is provided with ventilating bores.
By means of this combination of characteristics, it is achieved that the fibers are bundled well by means of a very small mouth of the fiber feeding duct. In this case, not all transport air taken in at the opening roller must flow through the mouth of the fiber feeding duct because part of this transport air is sucked off through the bypass opening. The amount of transport air to be removed from the spinning rotor is therefore reduced which leads to slower speeds in the overflow gap. As a result of the additional ventilating bores in the spinning rotor, it is achieved that the amount of air to be removed by way of the overflow gap is reduced further.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.